1. Field of the Invention
The present invention relates to a warm air generating apparatus for blowing warm air onto an object, a sheet feeding apparatus including the warm air generating apparatus, and an image forming apparatus including the warm air generating apparatus and the sheet feeding apparatus.
2. Description of the Background Art
In an image forming apparatus such as a printer, a copier, or a facsimile, gloss enamel paper having enhanced whiteness, film sheets, tracing paper, and so on are used as a sheet on which an image is recorded in addition to high quality paper and regular paper. These special types of paper exhibit a strong inter-sheet sticking force, and it is therefore difficult to prevent multi-feeding of the sheets. Hence, special measures must be taken in relation to sheet dispatch.
An upper face and a peripheral part of a stack of sheets housed in a sheet feeding cassette (sheet feeding apparatus) are exposed to outside air, and are therefore likely to contain a large amount of moisture. In other words, the upper face and side faces of the sheet stack swell due to moisture absorption, whereas the inside of the sheet stack contains a smaller amount of moisture than the upper face and side faces and therefore swells less. As a result, pressure in an inside space (an inter-sheet space) of the sheet stack may turn negative such that the sheets stick together.
A conventional sheet feeding apparatus includes a mechanism for blowing warm air onto the side face of the sheet stack to loosen the sheet stack by separating sheets that are stuck together prior to sheet feeding. For example, Japanese Unexamined Patent Application No. 2001-48366 discloses a technique for improving sheet drying efficiency by blowing warm air onto the side face of a sheet stack and appropriately adjusting the humidity of the warm air.
When a mechanism such as that described above for blowing warm air onto the sheet stack is employed, a warm air generating apparatus that typically includes an electric heater and an air blowing fan and is capable of generating a high-temperature air flow is used. In this type of warm air generating apparatus, the temperature of the electric heater is preferably detected accurately to achieve optimum temperature control of the air flow and prevent overheating of the electric heater. However, in a conventional warm air generating apparatus applied to a sheet feeding apparatus, sufficient measures have not been taken with respect to this point.